The establishment of the Old Swiss Confederacy in the Late Middle Ages resulted from a series of military successes against Austria and Burgundy. Swiss independence from the Holy Roman Empire was formally recognised in the Peace of Westphalia in 1648. The Federal Charter of 1291 is considered the founding document of Switzerland which is celebrated on Swiss National Day. Since the Reformation of the 16th century, Switzerland has maintained a strong policy of armed neutrality; it has not fought an international war since 1815 and did not join the United Nations until 2002.